Scientists have discovered the earliest fossils of mosses on Earth

Earliest restoration of bryozoans. Photo courtesy of Zhang Zhifei's team

A few days ago, Professor Zhang Zhifei of the Early Life Research Team of Northwest University instructed doctoral student Zhang Zhiliang to discover several millimeter-level micro-fossils in the clastic limestone of the Xi artemisia section of the Xiaoyang Section of the Xiaoyang Section of the Light shadow group in Xiaoyang Town, Zhenba County, Hanzhong City, Shaanxi Province. After the preliminary research of the research group, together with Glenn Bullock, a professor at Macquarie University in Australia and an adjunct professor at Northwestern University, and cooperated with scholars at home and abroad such as the Nanjing Institute of Geology and Paleontology of the Chinese Academy of Sciences, the British Natural History Museum, and the Swedish Museum of Natural History, it is believed that these microenvironments represent the earliest known bryophyte (bryophyte) fossils on earth. On October 27, the results of the research were published in the form of a long article in Nature.

Bryozoans are euphrasiacs with tentacle crowns, a class of aquatic groups of solid benthic animals, belonging to the typical "grassroots animals". The Cambrian explosion event, in the Earth's oceans 530 million years ago, suddenly exploded the early ancestor representatives of almost all living animals, including vertebrates, which were preserved vividly in the Cambrian fossil library. But the very important animal phyla in geological history, the moss phylum, has lacked a solid fossil record in the Cambrian period. However, after the Ordovician period 480 million years ago, the fossils of mosses became extremely abundant, so they are also considered to be the product of large Ordovician radiation.

With the support of the National Natural Science Foundation of China, Zhang Zhifei's team used scanning electron microscopy and X-ray tomography to analyze and found that these fossils appeared in a two-way thin plate-like network, and the two sides of the back were covered with epidermal cells secreting chitinia chambers. The insect chamber lacks obvious mineralization, alternating 5 or 7 columns in longitudinal direction, showing clear modular geometric features, clear and recognizable, symmetrical on both sides, and the overall shape is rounded. Fossil studies have shown that the delicate geometric distribution patterns and strict hierarchical systems of the fauna on both sides originated 530 million years ago and are an important ecological innovation in the Cambrian explosion.

After the maximum minimalist method of 52 features, 18 taxa and 2 outer groups and bayesian branch systematic analysis, it is shown that the fossil bryozoan represents the basal taxon of fossil and living bryozoans, which is the most primitive ancestor type.

The study pushed the geological history of the moss phylum from the Pre-Ordovician to the early Cambrian explosion, pushing forward the geology of bryozoites by at least 50 million years. The study found that the modular growth and community distribution of the animals on both sides were much earlier than thought, suggesting that modern mosses may have originated from gregarious ancestral types rather than monolithic ancestors. The discovery of bryozoans in the early Cambrian period further supports the three-act Cambrian outbreak hypothesis proposed by the team of Shu Degan, an academician of the Chinese Academy of Sciences, and further reveals the process of staged and explosive emergence of the three major animal sub-boundaries of basic animals, proto-mouthed animals and post-mouth animals over a period of 40 million years.

"The discovery of fossils in the argillary limestone of the West Artemisia section of the Lantern Formation suggests that Cambrian bryophytes are similar to later genera and are suitable for living in a clear hard-bottom environment, thus revealing the lack of bryozoan fossils in the specific fossil pool preserved in the mud shale." Zhang Zhifei said that the discovery provides new evidence for the formation of animal trees on Earth and the Cambrian explosion of life, showing that the study of specific fossils cannot fully reveal the historical process of life evolution in geological history, and other fossils are still needed to be constrained and supplemented. (Chen Bin, Zhang Xingyong)

Source: China Science Daily